Lets assume the setting is multiple civilizations all around the universe, each owning at least one of a planet, a huge mother space ship or a space fleet.

If for some reason there would be a conflict between two factions, how much sense would classical firearms (guns, assault rifles, ...), as we know them, in gravity-free zones do? If we watch this video, the last statement is "to be careful where you shoot, because you may end up hitting yourself" (due to the gravitational force of planets) - or your allies, in my case. So would it be logical, if classical firearms would not be "allowed" in space-fights, because of that?

Would it make more sense to rely on classical swords and/or martial arts? Or generalized, what other weapons (maybe some that I have not mentioned) or techniques could be used to fight your enemies?

Maybe you could avoid fighting in space, but there are always troublemakers, fight-hungry factions, not?

  • $\begingroup$ Lasers are pretty good for this. Less-affected by gravity, very fast, potentially transfers a lot of energy. Hand-to-hand probably doesn't make much sense. If the opponent is in a space suit of some sort, anything that compromises that suit is a good bet. $\endgroup$ – Sol Aug 30 '20 at 4:36
  • $\begingroup$ What do you mean by "classical firearm"? Do you mean specifically handguns and assault rifles or are you talking about kinetic weapons in general (including things like railguns, coilguns, etc.) $\endgroup$ – Dragongeek Aug 30 '20 at 17:36
  • $\begingroup$ What type of conflict are you talking about? There is a big difference between boarding actions and inter-ship warfare. Commonly in SF, boarding actions have characters use "indoor guns" which are loaded with things like plastic bullets to prevent accidentally shooting through to vacuum. Conversely, inter-ship battles typically occur over tens of thousands of kilometers $\endgroup$ – Dragongeek Aug 30 '20 at 17:38
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    $\begingroup$ Any ship that can't afford to run into the odd stray bullet can't afford to run into a micrometeorite either. As such, projectile weapons are likely only useful as point defense against missiles, or if you can hit your opponent enough times to overwhelm their mundane particle shielding. $\endgroup$ – Matthew Aug 30 '20 at 17:49
  • $\begingroup$ @Dragongeek Yes handguns an assault rifles. If there is a conflict, conflict can be everywhere. You got spies, traitors and other two-sided guys, fighting in parallel with the outer-ship conflict. Of course it is also possible to have only one of them occure at the same time. And I think I'm talking about both. How can you handle guns in ships? Outside? $\endgroup$ – rphii Aug 30 '20 at 17:50

What you want is: low momentum, high kinetic energy. That means you have to make to projectiles as fast as possible, which actually makes railguns (see "The Expanse") a pretty good and controlled choice for short to medium range combat. And (also see "The Expanse") yes, if you work more with them you may want a compensation for the recoil. For short range combat (carried by individuals), chemical firearms should do fine, although I think they should not be automatic in case ob being used in vacuum (Thermal problem). Lasers are impractical in short to medium range combat for the same reason they are impractical on earth (infrastructure + power used + efficiency). So i could imagine that lasers play a role in long range combat, mainly for the reason that they can not be maneuvered.

The hit precision (expressed as radius) of a target vessel for using the kinetic weapons by this would be:

r= 1/2 a_target * (distance/(v_projectile-v_target) - t_preparation)^2

Lets assume a railgun with 20km/s projectile velocity, a maximum acceleration in the orthogonal direction of the projectile path of 3 g and a target in 10km distance:

  • target accuracy 3m if the target can react immediatly
  • in the target needs 0.5 s t o react (e.g. flip in the right direction to survive the acceleration), it has not capability to void the hit (so actually, yes, that makes the decision to use railguns for ship defense in "The expanse" sound reasonable

It also tells us that if we are talking about distant ships no conventional kinetic weapons makes sense, as long as they can be detected, they can be avoided by accelerating.

(you could not even hit a 1km big ship from 1000km distance, even if they use only 0.1g to move out of the path).

So now we discussed the defense against kinetic weapons (radar + lidar + avoid the projectile). Lasers for long range sounds good, but i have my doubts - if you know the wavelength of the lase of the enemy, it pretty easy to construct lightweight high-efficiency mirror modules to cover your ships (maybe even something which looks like a solar sail).

Which shifts much of the combat to the ability to detect projectiles/missiles and align your defenses against long range weapons strategically, so that would probably mean that the real tech war would be taking place along radar, lidar and stealth technology (see "The Expanse") that you can use to detect kinetic weapons and hide your ship. So I would find it not unlikely (and here i think "the expanse" does not go far enough) that big fleets would not only be aircraft-carrier structure but would have drone networks traveling with them at ~100km-10000km distance, and potentially a lot of radar/lidar drones to fire out as consumption material in the 100s.

I would also think about proton/helium ion or plasma beams (you basically create a very localized solar flare) to damage and disturb electronics. I would also think that plasma could be uses to cloak the exact position of your ship.

  • $\begingroup$ Finally someone who doubts the efficiency of lasers to use them everywhere and has other explained opinions / methods! And nice explanation, that even I could understand it $\endgroup$ – rphii Aug 30 '20 at 17:45
  • $\begingroup$ Small conceptual note: Although there are thermal issues with setting a conventional rifle to full auto in a hard vacuum, one might consider disposable heat-sinking material as a supply complimentary to ammunition. Or just insulating several firearms and discarding them instead of reloading. The extra weight on a soldier's back is presumably offset by putting him in zero-g, and one surmises the cost would be negligible compared to the other sophistications of a space-faring society. $\endgroup$ – Eikre Aug 31 '20 at 10:42
  • $\begingroup$ You might want to take a look at Schlock Mercenary for some examples of drone clouds. Also guided missiles with casaba howitzer warheads would likely be extremely effective, but rather expensive. $\endgroup$ – Perkins Sep 3 '20 at 4:59
  • $\begingroup$ @Eikre Vacuum suits have to have a thermal management system to keep the occupant from cooking in their own body heat anyway. Extending that to include cooling for weapons or other tools is not at all unreasonable. $\endgroup$ – Perkins Sep 3 '20 at 5:00

Perfect Vectors don't happen:

I am not sure what kind of tech you are discussing, so I have limited my self to tech currently available - no ray guns.

In this scenario, the likelihood of shooting yourself in the back is insanely small. Space is huge, and vectors incredibly variable. If you were trying to shoot yourself, I doubt you could do it. A planet is gigantic, and it would be comparable to dropping a baseball from orbit by hand and expecting your kid in a park on the surface to be able to catch the ball.

Martial arts in zero G has already been addressed (Styles of Melee Combat developed in microgravity)The movement of objects in zero gravity is predictable, BUT the movement of people constantly thrusting and vectoring makes connecting with someone tricky, and means that pulling back an arm to swing a sword creates an equal and opposite rotation of you. A kick to an opponent pushes them away, and pushes you away as well. As hard as it would be to hit someone, once you did the fight would shift apart again. The unpredictable nature of multiple velocities and vectors means hand to hand in zero g would be incredibly frustrating. On the other hand, it might create unique opportunities - drive back opponents, use a counter weight in the opposite hand to adjust your rotation, etc. I don't see it as very effective, but I could imagine training to compensate.

In vacuum, you would find guns to still be valuable. Explosive decompression is a threat in space, but frangible bullets dissolve into tiny grains on impact with hard surfaces, dissipating the force, but still ripping intact through soft targets - like space suits and people. Even in vacuum, guns can fire, contrary to popular myth. A projectile from a gun still hits your opponent with great force to a tiny area, causing serious harm. Depending on the mass of the person and weapon firing, the effect of firing a gun could be noticeable or negligible, but if you are in a zero-G environment, you would hopefully have some form of thruster to compensate for changes in your velocity. If you don't, a gun is even more valuable - as a thruster to get you moving, not a weapon.

If you don't want to deal with changes to your velocity, there's a slightly unconventional but existing gun that performs well - the gyrojet. This is a mini-missile launcher, where the projectiles do the thrusting - little or no recoil, because the projectile has thrust, and the gun isn't exploding.

You can separate the shooting from you all together by deploying drones with projectile weapons. These miniature remote control spaceships or autonomous robots can be tiny, deploy guns, be armored, and be disposable. The people stay still while remoting around drones to kill people or other drones. Because of the nature of zero G, grenades could be fiendishly tricky but effective. A grenade with a motion-sensor can be lightly pushed in the direction of enemies and it can move fast OR slow towards opponents. Remote triggers could mean the grenade IS a drone of sorts, with it's own tiny thrusters, and it can explode on command. It could create concussion effects (if there is air) or use shrapnel. Fire can consume oxygen, and poison (gas, contact agent, etc.) can kill people, destroy air systems, or splatter toxins on surfaces, making areas temporarily uninhabitable. Even adhesives and sticky weapons would be highly effective in space, as the range of a stream of adhesive foam is almost infinite, and superglue bombs jam equipment or make opponents stick to the next wall the touch, all without the pesky interference of gravity.


The "you may end up hitting yourself" case is about as likely as headshotting yourself by firing upwards on the planets surface and having it come back down. The chances are vanishing small, and dependant on orientation and inclination and exit velocity and what type of orbit you're in and all sorts of factors.

Some big machine gun turret firing lots may eventually come across this problem, however a bit of software patching and it can avoid establishing bullets in dangerous orbits.

However bullets fired in orbit, that get in the sweet spot of a stable orbit, may potentially stay up there for thousands of years, they may take out civilian vessels hundreds of years later. This could be the equivalent of an "anti landmine" movement. However rogue nations still use landmines because they're effective and useful, so they'll still fire bullets regardless of treaty.

Bullets would also contribute to https://en.m.wikipedia.org/wiki/Kessler_syndrome

You could also create a Kessler syndrome intentionally on an enemy planet. Just put millions of bullets in orbit such that they intersect all their launch trajectories. They'll never be able to launch again.

Theres on other issue with guns in orbit. Guns do fire in space, but they dont cool down. You'll get a magazine out and then itll be too hot to touch. Youd need some impressive cooling system, eg backpack radiator, to fire an automatic weapon in space.

For actual realistic weapons, in space conflict;

I'd go missiles as my first weapon. Able to manoeuvre in orbit themselves and can find, follow, and destroy a ship. Cant use normal air missiles (fins dont work) but nozzle angling can work well.

Ship mounted Gatlin guns are plausible; they have the cooling system of the ship to support them.

You can also do some amazing sneak attacks; Bullets that enter orbit also have another advantage, they dont need line of sight to hit. You can scout out an enemy ship, manoeuvre to some hidden spot in orbit, fire a precisely calculated salvo, and then leave orbit, hours later, your bullets will impact the ship.

To destroy a surface target, nuke missiles are an obvious favourite, but may I suggest "Rods from God", where you accelerate a stick of dense metal straight down into the planet. They're cheap to make and thousands can be launched at once. No fallout either.

Person to person combat is more likely to be small saboteur teams. Magnetic mines and an airgun is probably what they're going in with.

A crowbar with a sharpened tip will rip open a space suit or pull out tubes and cables. That's a good close quarters weapon if they get desperate.

  • $\begingroup$ "you may end up hitting yourself" - "or your allies". but for the rest, thanks for the thoughts. $\endgroup$ – rphii Aug 30 '20 at 6:34
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    $\begingroup$ One comment on stable orbits: No bullet has a stable orbit close to a planet. Compared to a satellite, a bullet has a tiny ratio of mass to frontal area, so its orbit will decay much quicker than that of a satellite. If you have a satellite on an orbit that decays within 20 years, you can expect a bullet in the same orbit to decay within a single year. As such, bullets will quickly be cleaned from the most relevant low orbits. They would be a much more serious threat in higher orbits that don't decay in any appreciable time frame, but the vast majority of satellites will always be in low orbit $\endgroup$ – cmaster - reinstate monica Aug 30 '20 at 8:39
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    $\begingroup$ @rphii If you hit your allie with an infantry weapon it's either because you think they are the enemy or they are * directly behind* your enemy. The first case is a non-issue today. The second is an issue in certain situations (for example how ambushes are set up) and are provided for by doctrine and common sense. I highly doubt these rather rare cases would make up for the problem of getting shot dead very commonly. $\endgroup$ – lidar Sep 1 '20 at 0:40

Every responsible shooter in the real world knows that any bullet will come down, eventually. A pistol might have an effective, aimed combat range of 25 or 50 meters, but the bullet can retain lethal force for a kilometer or more. On Earth, militaries make plans how that can be avoided for the big guns. Google Fire Support Coordinating Measure and no-fire area.

In space, the math simply becomes more complicated, but that's what computers and databases are there for. You could even use that and shoot something on the other side of the planet if you can aim precisely enough. And if you miss, the bullet becomes just another piece of orbital debris to annoy the civilian users of space.


In it's current format the question is simply too large and broad and vague to answer.

Here are some points to further show that.

  • There are several civilizations with unknown abilities and unknown tech and unknown economy and numbers and everything else. How can we answer you?
  • You go to war with the army you have. Race A might have lasers but you got firearms. Guess what weapons your infantry is using?
  • The advancement of these civilizations will vary in tech and even theory to the point of making none capable of giving you an answer. For example in warhammer 40K we know nids are a hivemind "bugs" race which uses biological matter to make all their stuff. So we know their strategy is to throw millions of their lesser bio weapons, think zerg rush, to soften the enemy. Contrast that with the elder who are so rare and depleted that they manipulate events and other races to fight their wars.
  • Where are the fights actually located? This is the biggest factor. Imagine boarding operation then imagine large fleets exchanging fire then oppose that with good old ground assault on the planet. So knowing where the fights is going to happen we might consider something like firearms for planet action and special weapons for 0 G environments. But we don't know anything about that. even today terrain is important.
  • Who are fighting and for what purpose? Are we using humans as soldier or drones or fixing batteries on star ships or robots or what?
  • Your video example is good to demonstrate abstract ideas. Are space fights going to be in 0 G with a guy standing alone in space shooting a gun? I doubt it. You want to translate that into a battlefield though right? Well then like I said before where is the fighting to begin with.
  • I'd also argue that by the time you have FTL capable empires who want to wage wars then you have automated and highly advanced fighting machines that can wage wars for that civilization with minimal sentient input.
  • Tell us more on what you want to accomplish as well.
  • "Would it make more sense to rely on classical swords and martial arts" Actually context dependent. Imagine a large space ship, large city like, with limited access to guns and bullets. People in there, lets assume numbering in the millions, would have to relay on other means to do violence as they just don't have access to weapons, being in space and having limited access to it to begin with.
  • But you can also create your own unique race with firearms disruption fields who go around wielding swords. They can follow the ancient honorable ways of their ancestors and use swords and their super advanced suits which stops bullets and other projectiles and allow them to close in and kill the enemy in a proper way. Highly feared and respected in the galaxy. Many others tried to copy them and attempted to counter them in that way. Hilarity ensues though when a practical commander decides to counter them by massing small arms fire or just throwing more bullets at them until their tech is fried and they are ripped apart by our good old automatic rifles. Remember my friend Sir Isaac Newton is still the deadliest son of a b*tch i space. Also chemistry in there for good measure.

Anyway I don't mean to be rude or unhelpful. I'd love to help and try to figure out what fits your world and can meet your requirements. But in that state we can't.

Update after your comments.

There are basically 2 large types of factions.

  1. FTL capable, planet killer factions.
  2. Stuck on one planet faction.

There is no war between the two. From space you can mess up the entire planet. No problems.

War between the first type would be costly and extended. However there might be a scenario where faction A is still category 1 but only got one planet or base.

However type 1 can also be empire like, think Warhammer 40K.

And I will try to make just points on warfare but limit it practical solutions and try not to stray from your original post.

  • Automated warfare is the norm. There is 0 need for such an empire to send a single soldier into a battlefield. If they are FTL capable then it should not be a problem to be able to manufacturers millions of war machines.
  • Ship to ship engagements is the norm. It is unlikely to ever resort to boarding or actually need infantry. This is because ships can have planet killing weapons and so massing a trillion soldiers around a planet is like farting in the general direction of a tank.
  • What is the shape of the fighting machines? I always say this: plasma firing anti grav tank several a city block sized monstrosity. Add void shields, an army of drones for CQC, anti air capability, instant teleportation and shove an AI or AI level brain in there then connect it to the mother ship. That's it. Not a single soldier. Also it can function perfectly well on it's own and has like the entire warfare history of the galaxy.
  • 10000 lifespan of a creature would probably mean they don't produce as fast as humans. This race would then have to be extra careful. Like construct their whole society and life in a way they are using tech for everything. But even then they are not different as all other faction fight from orbit.
  • Is it more likely for factions to fight lower tier factions than comparable factions. Just because of the sheer amount of absurd powers they have. Think of nuclear deterrence and multiply it by 90000
  • 0G fighting? Unlikely. The enemy ship would either be ripped apart by your own weapons or rip you apart. Boarding seems absurd, you can get away with it buy use loads of context. Even then they would be still gravity. But even if there is no gravity does that change anything? No. You still want to kill the enemy and fighting in a ship means that the hull gets peppered, that's all. If you can't use plasma then even firearms still works fire. You are not firing in absolute vacuum.
  • Basically any fighting in the universe would happen around a thing that either have artificial gravity or large enough to have a gravity well of it's own. Even if not you are NOT worrying about anything like that.
  • The usage of MOAR firearms to cheaply counter the enemy could be done. But there is always a matter of resources to effectiveness. That is if plasma is the only viable option to counter enemy infantry, which is not even a thing anymore but whatever, then just throwing resources at firearms is absurd. But You can play around with specific contexts and all that.
  • You use the most effective, including cost by the way, means of disposing the enemy. The army is built upon win this engagement and then we will think of the other. Simply look at the cold war arms race. Or think of it this way. I'm worried about low gravity and firearms so I issue less effective weapons to my soldiers. The enemy do not worry about that and they issue the most effective weapon which does have the potential to hurt them but they don't care. My dudes get decimated in every engagement while doing little damage, and the side casualties of the enemy because of their weapons are acceptable. Not realistic. Just switch to the most effective and deal with whatever problem later.

I know it seems to challenge the idea and it might does. Because FTL just equals destroy it from orbit and just use machines. So infantry is not a thing any more. Warhammer 40K gets away with a lot of things but it is actually both science fantasy and rule of cool and internally consistent.

Hope it helps

  • $\begingroup$ I’ll try to address every point (in order, but I numbered it). Correct me if I understood anything wrong or if an answer is not enough. 1.1 Abilities: Normal Human things. (No magic) 1.2 Tech: They essentially can do FTL-travel with spaceships. Just like on earth, there may be some civilizations specialized in science-, good-production, spaceship-production, etc... 1.3 Economy: Similar to FTL-travel, there is FTL-trading. But how that works is not the topic of my question. $\endgroup$ – rphii Aug 30 '20 at 6:24
  • $\begingroup$ 1.4 Numbers and everything else: People are scattered all around the universe, even beyond the observable universe and potentially can grow up to over 10000 years old (how that works is, again, not topic of my question). The humans are in groups/civilizations for the same reason as we are in different continents, cities, etc: Either they are born into there and make a living, or they share the same interests and make a living. 2.1 It’s more about factions than races. What weapons they may choose is the topic of my question, actually. $\endgroup$ – rphii Aug 30 '20 at 6:25
  • $\begingroup$ 3.1 There is an FTL-network, so knowledge should be pretty much equal all over the universe. 3.2 Tech differences are pretty much nullified due to the FTL-network and FTL-transport. 4.1 That’s what I meant with “techniques”. One of my techniques would be something like: Faction A takes faction B’s planet hostage. If we go further in how the plot goes, we land on the storytelling-exchange. $\endgroup$ – rphii Aug 30 '20 at 6:25
  • $\begingroup$ 5.1 I thought I said “a conflict between two factions”, so the purpose is not really specified. But if you want a purpose, maybe some want one of the things they own: “each owning at least one of a planet, a huge mother space ship or a space fleet”, again, this would belong to the storytelling-exchange. 5.2 The second question is similar to my question as to what “techniques” there could be. 6.1 Would, again, belong to the storytelling-exchange, in my opinion. 7.1 That is an answer of your side for once, and one that I have not thought about, so thanks. $\endgroup$ – rphii Aug 30 '20 at 6:26
  • $\begingroup$ 8.1 I want to see what others think about “firearms in space”. Every answer then automatically is one inspiration, one thought, one idea more. That is the purpose of this exchange, no? 9.1 Similar to previous questions of yours, that I mostly answered and that may solve this specific problem of yours. 10.1 Thanks for this thought. $\endgroup$ – rphii Aug 30 '20 at 6:26

As of 2013 there were estimated to be 670,000 pieces of debris in Earth orbit between 1 and 10 cm in size.

Once a bullet leaves the immediate vicinity it becomes just another piece of orbital debris: a muzzle velocity of a few hundred m/s is actually quite small compared to orbital velocities measured in km/s. So a few people with guns are not an issue.

Of course if large scale war causes people to start spraying machine guns around indiscriminately then the debris field starts to mount up. World War II saw tens of billions of rounds fired, and if that happened in LEO it would definitely be an unhealthy environment. On the other hand if it happens in interplanetary space then the odds of being hit become much lower (as Douglas Adams said, "Space is big. Really big. Vastly, hugely, mindbogglingly big"). So a lot of the answer depends on where the action takes place.

More important are capital ships. The destruction of even a small ship would create vast amounts of orbital debris at every scale from sub-millimetre up to tens of metres. Compared to that bullets look pretty trivial. If your antagonists have the technology to deal with that then kinetic rounds are not an issue for their ships. And if they have active measures for kinetic threats then its hard to see how the same technology is not also an offensive weapon.

So the only role for kinetic firearms would be interpersonal combat. Unless you see boarding parties being a regular thing its hard to see why anyone would need to do this.


I think the series Mobile Suit Gundam addresses space combat well.

Mobile Suits use a variety of ranged and close combat weapons, from simple axes to beam sabers, and from bullets and lasers to guided missiles.

For close combat in micro-gravity, Mobile Suits use multiple thrusters, which often have thrust vectoring, to control themselves and stay engaged.

Collateral damage and misfires are always possible... But “shooting yourself in the back” is extremely unlikely because the ammunition would have to be released at orbitally stable velocity, along an orbital vector, and then the person whose fired it would have to adjust themselves to remain in the orbital path of said ammunition.


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